This invention relates generally to oceanography, and more particularly to a digital method and apparatus for generating a contour map of the ocean floor using acoustic pulses.
The invention has utility in the generation of oceanographic data for both naval and civilian purposes, and particular utility in the analysis of ocean bottom topology in the search for petroleum and other natural resources.
Currently, there are many ways in which a map of the contour of the ocean bottom can be generated from reflections of acoustic pulses. One such system, offered by General Instrument, Inc. of Westwood, Mass., is known as SEA BEAM. In typical ocean surveying systems, such as SEA BEAM, a high intensity acoustic pulse (typically using a carrier of 12 Khz.) is directed toward the ocean bottom. By measuring the angle of acoustic reflections off the ocean bottom, and their delay times, the system is able to construct a depth profile. In general, in these prior systems, the direction of a returning acoustic pulse is determined by establishing a set of predetermined angular intervals, using beam-forming techniques at the receiving sensor or sensors. The direction of the arriving pulse is determined by the particular beam in which its amplitude is greatest.
U.S. Pat. Nos. 4,207,620 and 4,561,076 are examples of typical ocean bottom scanning systems.
U.S. Pat. No. 4,207,620 describes an oceanographic mapping using a wide-swath beam athwartship beam in which beam-forming is carried out at the receiver by multiple transducers and delay lines. The beams are formed successively by steering the transducer array by control of the delay lines.
U.S. Pat. No. 4,561,076 describes a sonar method and apparatus for mine detection in which a narrow, fan shaped transmitting beam is transmitted from a vessel located forward and to one side of a receiving vessel and at a predetermined height from the bottom. A beam former is used together with an echo equalizer which associates the echoes with the reflection centers from which they have been generated. The echo equalizer associates time windows with the receiving sectors established by the beam former.
Prior systems capable of producing ocean bottom maps with high resolution and accuracy are comparatively expensive. They are also slow and expensive to operate, since they provide high resolution only over a comparatively narrow area of the ocean bottom.